The present invention relates generally to pulse shaping and amplifying circuits and more particularly to such a circuit which is highly energy efficient. This invention finds particular application as a gate pulse driver for periodically rendering thyristors conductive.
There are many applications for pulse shaping and amplifying circuits with one very common useage being that of providing gating or triggering signals or pulses which serve to render a thyristor conductive. A thyristor, the most common form of which is the Silicon Controlled Rectifier (SCR), is a three terminal semiconductor device having anode, cathode and gate electrodes which is placed into the connective state by the simultaneous application of a forward bias voltage between the anode and cathode and a gating signal applied to its gate electrode. Once a thyristor achieves conduction, it will normally remain in that condition until there exists a zero or reverse voltage bias between its anode and cathode terminals for a period of time sufficient to permit the current through the thyristor to decrease to substantially zero.
One common type of pulse shaping and amplifying circuit employs a charge storage means, usually in the form of a capacitor, to develop an electrical charge. Once the capacitor has been charged, through suitable switch means, mechanical or electrical, it is permitted to discharge through the load (e.g., a thyristor gate driver) resulting in a pulse of electrical power being delivered to the load. By the proper sizing of circuit component and values, the pulse produced is properly shaped and of a magnitude and duration for the desired function.
In many instances the pulse shape, magnitude and duration requirements dictate that the total electrical power of the pulse far exceeds that normally required by the load. For example, the specified pulse requirements for a thyristor gate driver often far exceed the power required to actually gate the thyristor on; the excess power in the pulse being in the nature of a safety factor to insure thyristor conduction. In these cases, it is apparent that unless this excess power is in some way recovered, the results are wasted energy and the requirement of removing undesirable heat.